1. Field of the Invention
The present invention relates to an X-ray condenser for condensing X-ray diverging from an X-ray source to a small point, which is suitable for use in an X-ray diffraction apparatus such as an X-ray micro-diffraction apparatus or an X-ray microscope for measuring X-ray diffraction by irradiating a very small region of a sample or a very small sample with X-ray. Further, the present invention relates to an X-ray apparatus constructed with the same X-ray condenser.
2. Description of the Related Art
In an X-ray micro-diffraction apparatus, a micro-area of a sample, etc., is irradiated with an X-ray beam having very small cross sectional diameter and an X-ray information such as diffracted X-ray information, from the sample existing in a field of the irradiation is measured by an X-ray detector. On the other hand, in an X-ray microscope, values of X-ray absorption at discrete positions of a sample under measurement is measured by scanning the sample with an X-ray beam having small cross sectional diameter and detecting intensities of the X-ray transmitted at the respective positions of the sample by an X-ray detector.
In the X-ray apparatus such as the X-ray micro-diffraction apparatus or the X-ray microscope, mentioned above, it is necessary to irradiate a micro-area of a sample with an X-ray, which diverges from an X-ray source and is, preferably, converged on said micro-area. An X-ray condenser is used to converge, namely condense, the diverging X-ray. An example of the X-ray condenser is disclosed in Japanese Patent Application Laid-open No. H8-128970. The disclosed X-ray condenser utilizes an inner surface of a cylinder as an X-ray reflecting mirror and X-ray is condensed to a micro-area by making the inner surface of the cylinder curved.
The disclosed X-ray condenser has a very simple construction and can condense relatively intense X-ray to a micro-area. However, there is a limit in reducing the cross sectional diameter of condensed X-ray. For example, it is very difficult for the disclosed X-ray condenser to reduce the diameter of irradiation area to a value smaller than 10 xcexcm.
An object of the present invention is to provide an X-ray condenser capable of condensing X-ray to a very small spot.
Another object of the present invention is to provide an X-ray apparatus capable of performing an X-ray measurement with very high spatial resolution.
According to the present invention, in order to achieve the above mentioned objects, an X-ray condenser for condensing X-ray radiated from an X-ray source to a micro spot is featured by comprising parallel beam forming means for collimating a diverging X-ray from the X-ray source to a parallel X-ray beam and a zone plate disposed in a downstream side of the parallel beam forming means in a propagating direction of the X-ray and constructed by alternately arranging X-ray transmitting bands and X-ray shielding bands.
The zone plate is an X-ray optical component for condensing parallel X-ray beam to a point remote from it by a specific focal distance. Therefore, when a parallel X-ray beam is formed by the parallel beam forming means and the parallel X ray beam is incident on the zone plate, it is possible to condense the X-ray to a micro spot having diameter smaller than 10 xcexc, which was impossible by the conventional X-ray condenser.
For example, as shown in FIGS. 4(a) and 4(b), the zone plate 11 may be formed by alternately arranging X-ray transmitting bands 12, which allow X-ray to pass through, and X-ray shielding bands 13, which do not allow X-ray to pass through. In the structure of the zone plate shown in FIGS. 4(a) and 4(b), the X-ray transmitting bands 12 and the X-ray shielding bands 13 are circular. The zone plate 11 can be manufactured by forming the X-ray shielding bands 13, which is patterned in a predetermined manner, on an X-ray transparent substrate 14 by a suitable patterning method such as photolithography. In such case, the X-ray transmitting bands 12 are formed by portions of the X-ray transparent substrate 14, which exist between adjacent X-ray shielding bands.
The X-ray transparent substrate 14 may be formed of, for example, silicon nitride (Si3N4) or boron nitride (BN). The X-ray shielding bands 13 may be formed of, for example, gold (Au), tantalum (Ta) or nickel (Ni). The number of zones each including a pair of the X-ray transmitting band and the X-ray shielding band is set to, for example, in the order of 300 to 400.
Since the index of refraction of electromagnetic wave in X-ray region is close to xe2x80x9c1xe2x80x9d, X-ray cannot be focused by using an optical lens for a visible light. The zone plate is used in X-ray region as a substitution for the optical lens. The zone plate takes in the form of, for example, a circular diffraction lattice with which X-ray can be focused. The zone plate having 100 or more zones can be treated in substantially the same manner as a lens used in a usual refractive optics.
In FIG. 4(b), X-ray R0 radiated from an X-ray source F passes through the X-ray transmitting bands 12 to a condensing spot P. Widths of the X-ray transmitting bands and the X-ray shielding bands are set such that an optical path length of X-ray passing the (m)th X-ray transmitting band is shifted from that passing through the (m+1)th X-ray transmitting band by a wavelength of the X-ray so that all X-ray beams reaching the condensing spot are intensified each other. Thus, the condensing spot P becomes equivalent to a focusing point of an optical lens.
Incidentally, in the present invention, the zone plate may be the so-called phase zone plate. That is, the usual zone plate utilizes the phenomenon that X-ray beams passed through the X-ray transmitting bands are intensified each other by interference so that the X-ray beams are focused. On the other hand, when the thickness of the X-ray shielding bands is reduced such that X-ray can pass therethrough with phase thereof being shifted by a half wavelength, X-ray passed the X-ray shielding bands and X-ray passed through the X-ray transmitting bands are intensified each other by interference to thereby increase the intensity of output X-ray. The zone plate having the latter property is called xe2x80x9cphase zone platexe2x80x9d.
In the X-ray condenser according to the present invention, it is preferable to provide spectrometry means capable of picking up X-ray component having a specific wavelength from X-ray containing a plurality of different wavelength components between the parallel beam forming means and the zone plate.
In general, there is the problem of chromatic aberration in the zone plate. That is, when parallel X-ray incident on the zone plate contains X-ray components having different wavelengths, the condensing spot of the X-ray is blurred correspondingly to the wavelength difference, so that it becomes difficult to form micro-X-ray beam having finely defined cross section. However, by monochromatisation of the X-ray incident on the zone plate by means of the spectrometry means, it is possible to reduce the chromatic aberration to thereby prevent the X-ray condensing spot from being blurred.
The spectrometry means is not limited to a spectroscope having a specific structure or to a substance having a specific structure. For example, the spectrometry means may be constructed with using analyzing crystal.
In the X-ray condenser according to the present invention, the parallel beam forming means may be parabolic parallel beam forming means in which diverging beams are made parallel either in horizontal or vertical direction, by utilizing a parabolic surface. By utilizing such parabolic surface, it is possible to form exactly parallel X-ray beams with a simple construction.
In the X-ray condenser according to the present invention, the parallel beam forming means may be parabolic parallel beam forming means in which diverging beams are made parallel both in horizontal and vertical directions, by utilizing a parabolic surface. By forming parallel X-ray beams parallel both in the horizontal and vertical directions by utilizing such parabolic surface, it is possible to form more intense X-ray beam having rectangular cross section compared with the described construction for forming X-ray beam parallel in only one of the horizontal and vertical directions.
In the X-ray condenser according to the present invention, the parallel beam forming means may be constructed with a parabolic reflection mirror capable of reflecting X-ray by a parabolic surface or a multi-layered parabolic film mirror capable of reflecting X-ray by diffraction by a multi-layered film formed on a parabolic surface.
As shown in FIG. 2(a), the parabolic reflection mirror la may be formed by machining a surface of a member 2 of such material as glass or metal capable of reflecting X-ray to a parabolic surface H and mirror-finishing the parabolic surface H. Incidentally, the parabolic surface H has a suitable width and extends in a direction perpendicular to the plane of FIG. 2(a).
Alternatively, as shown in FIG. 2(b), the parabolic reflection mirror 1b may be formed by machining a surface of a substrate 3 of such material as glass, metal or resin to a smooth parabolic mirror surface H and forming a reflection film 4 of metal on the smooth parabolic mirror surface H. In such case, the metal reflection film 4 may be formed of Au, Ni or platinum (Pt). As the forming method of the metal reflection film 4, any known film forming method, for example, vapor-deposition or sputtering, may be used. Incidentally, the parabolic surface H has a suitable width and extends in a direction perpendicular to the plane of FIG. 2(b).
In the parabolic reflection mirror 1a shown in FIG. 2(a) and the parabolic reflection mirror 1b shown in FIG. 2(b), the X-ray source F is positioned at a focal point of a reflection surface of the parabolic reflection mirror 1a and 1b, that is, the parabolic surface H. Therefore, when X-ray R0 diverging from the X-ray source F is incident on the reflection surface of the parabolic reflection mirror 1a and 1b, the X-ray R0 is reflected, in more detail, fully reflected by the parabolic surface H as parallel X-ray beam
As the method for forming the parallel X-ray beam, a collimator utilizing a slit or a pinhole has been known widely. In such conventional method, however, it is difficult to form intense parallel X-ray beam with high degree of parallelism. On the contrary, according to the present method using the parabolic reflection mirror 1a or 1b, it is possible to form intense parallel X-ray beam with high degree of parallelism.
On the other hand, as shown in FIG. 3, the multi-layered parabolic film mirror 6 can be formed by machining a surface of a substrate 3 to a smooth parabolic mirror surface H and forming a multi-layered film 7 on the smooth parabolic mirror surface H. The substrate 3 may be formed of, for example, single crystal of silicon (Si) or stainless steal.
The multi-layered film 7 is formed under condition that a plurality of heavy element layers 8 and a plurality of light element layers 9 are laminated alternately and a surface thereof on which diverging X-ray R0 from the X-ray source F is incident is the parabolic surface H. The formation of the respective layers may be performed by any suitable method, for example, sputtering.
By piling up a plurality of unit laminations each including the heavy element layer 8 and the light element layer 9, periodically, it is possible to diffract a specific X-ray, for example, CuK xcex1 ray, efficiently. As a result, it becomes possible to obtain intense X-ray at an output side of the parallel beam forming means. Further, by forming the surface of the multi-layered film 7 as the parabolic surface H, it is possible to diffract, that is, reflect incident X-ray on the whole surface to parallel directions to thereby obtain exactly parallel beams. In other words, very intense monochromatic parallel X-ray beam can be obtained by using the multi-layered parabolic film mirror 6.
When X-ray is to be fully reflected, it is necessary to direct incident X-ray at a small angle with respect to all reflection surfaces, that is, to reduce glancing angle. Therefore, intensity of X-ray to be condensed may be reduced. However, since it is possible to set the glancing angle to a large value in the multi-layered film 7 designed to diffract X-ray at the parabolic surface, it is possible to collect intense X-ray at the condensing spot.
Incidentally, in order to diffract X-ray in the respective layers, thickness t1 of the unit lamination of the heavy element layer 8 and the light element layer 9, that is, thickness of the unit lamination for one period, on the X-ray incident side is smaller than thickness t2 of the unit lamination on the X-ray output side. For example, t1 and t2 may be set to t1≈30 xc3x85 and t2≈40 xc3x85.
As the heavy element, for example, tungsten (W), etc., may be considered and the light element may be, for example, Si, carbon (C) or boron carbide (B4C), etc. Incidentally, the number of layers of the unit lamination is not limited to 2. For example, 3 layers or more of different elements may be included in the unit lamination.
In the X-ray condenser according to the present invention, in which diverging X-ray is made parallel beams in both the horizontal and vertical directions by the parallel beam forming means, it is preferable that the X-ray source is of the point focus type, X-ray from which has an area whose vertical width is substantially equal to horizontal width.
Alternatively, the X-ray source may be a line focus type, X-ray from which has an area whose horizontal width is larger than vertical width, or vice versa. However, when the line focus type X-ray source is used to make diverging X-ray parallel beams in both the horizontal and vertical directions, a resultant parallel beam is only a portion of the diverging X-ray and the remaining X-ray is not formed to parallel beam and consumed uselessly. On the contrary, when the point focus type X-ray source is used for the same purpose, it is possible to form diverging X-ray to parallel beams in both directions effectively.
In the X-ray condenser according to the present invention, it is preferable to provide a casing for air-tightly defining a space from the parallel beam forming means to the zone plate and evacuation means for discharging air out of the casing.
When the casing is evacuated by the evacuation means, it is possible to prevent X-ray condensed through the parallel beam forming means and the zone plate from being attenuated by air scattering to thereby condense intense X-ray to a micro spot. The evacuation means can be constructed by, such as a device for drawing air within the casing to reduce internal pressure thereof or a device for replacing air within the casing with helium.
An X-ray apparatus according to the present invention, which includes an X-ray source for radiating X-ray, an X-ray condenser for condensing X-ray from the X-ray source to a micro spot or a micro specimen and X-ray detection means for detecting X-ray from the specimen, is featured by that the X-ray condenser is constructed with the above-mentioned components. As the X-ray apparatus, an X-ray micro-diffraction apparatus or an X-ray microscope may be considered for example.
According to this X-ray apparatus, intense X-ray can be condensed in a very small area having diameter of, for example, 10 xcexcm or less without blur, so that it is possible to irradiate a very small portion of a specimen or a very small specimen with intense and well defined beam to thereby obtain a result of measurement highly reliably with high spatial resolution.